Heat transfer in coolant circuits can be enhanced by maintaining the coolant in a nucleate boiling heat transfer regime. However, during nucleate boiling heat transfer, the heat flux can reach critical heat flux (CHF) at which point further increases in heat flux cause a departure from nucleate boiling (DNB). This phenomenon is illustrated graphically in FIG. 1. When the coolant reaches departure from nucleate boiling, an increase in heat flux can cause the coolant to jump instantly to a film boiling state in which the temperature Ts of surfaces in the coolant circuit can rise rapidly to several hundred or thousands of degrees above the saturation temperature Tsat of the coolant. Consequently, surfaces in the coolant circuit can be damaged, thus causing damage or catastrophic failure of the device being cooled.
Due to the benefits of nucleate boiling heat transfer, efforts have been made use nucleate boiling heat transfer while avoiding damage from film boiling. For example, in U.S. Pat. No. 4,474,231 to Staub et al., the entirety of an immersed surface is provided with a plurality of cavities configured in a manner intended to avoid film boiling at the surface. Although the Staub et al. arrangement may be advantageous in preventing film boiling at the surface, the Staub et al arrangement is subject to improvement since not all surfaces in a coolant circuit are equally susceptible to the high heat flux that results in departure from nucleate boiling. Thus, use of the Staub et al. approach can incur more expense than needed to achieve the desired result of avoiding film boiling. In addition, the Staub et al. arrangement only increases the critical heat flux associated with departure from nucleate boiling but does not change the superheat gradient during nucleate boiling heat transfer. Moreover, the Staub et al. approach is not useful if forming cavities on the parent surface to be cooled is not possible or not practical.
Accordingly, there is a need for a cost-effective and flexible cooling arrangement in which a surface configuration tending to inhibit boiling state transitions (e.g. transitions to film boiling) is applied to only selected surfaces in the coolant circuit that are considered susceptible to film boiling.